Method for maintaining flatness, flatness maintaining unit and device, and disc manufacturing method and device

Abstract

A method is presented for maintaining a plate member in a flat state, including the steps of placing the plate member on a surface of a supporting member, the surface of the supporting member being in a flat state and having at least one hole penetrating through the surface, and sucking air from a back side of the surface of the supporting member to generate an airflow flowing from a front side of the surface towards the back side thereof via the hole so as to retain the plate member on the surface of the supporting member. In this manner, the plate member, such as disc substrates adhered together by using an ultraviolet curable composition, can be accurately maintained in a flat state without damaging the surface thereof.

What is claimed is:  
     
         1 . A method for maintaining a plate member in a flat state, comprising the steps of: 
 placing said plate member on a surface of a supporting member, the surface of said supporting member being in a flat state and having at least one hole penetrating through the surface, and    sucking air from a back side of the surface of said supporting member to generate an airflow flowing from a front side of the surface towards the back side of the surface via the hole so as to retain said plate member on the surface of said supporting member.    
     
     
         2 . A method for maintaining a plate member in a flat state according to  claim 1 , wherein 
 said plate member is a disc substrate, and the airflow is generated at least at an inner periphery portion and an outer periphery portion of said disc substrate.    
     
     
         3 . A method for maintaining a plate member in a flat state according to  claim 1 , wherein a surface roughness Ra of the surface of said supporting member is about 3.0 μm or less.  
     
     
         4 . A method for maintaining a plate member in a flat state according to  claim 1 , further comprising the steps of: 
 retaining said plate member on the surface of said supporting member at a first point, and    removing said plate member from said supporting member at a second point after moving said supporting member along a transfer path.    
     
     
         5 . A method for maintaining a plate member in a flat state according to  claim 4 , further comprising the step of: 
 placing another plate member on the surface of said supporting member at the first point after said plate member is removed from said supporting member at the second point so as to repeatedly use said supporting member.    
     
     
         6 . A method for maintaining a plate member in a flat state according to  claim 5 , wherein 
 a plurality of said supporting members, which retain said plate member, are disposed on said transfer path at the same time.    
     
     
         7 . A method for maintaining a plate member in a flat state according to  claim 4 , wherein 
 an electric fan is integrally provided with said supporting member, and    contacting electrodes which supply electric power to said fan are disposed on said transfer path so that the airflow is generated by operating said fan.    
     
     
         8 . A method for maintaining a plate member in a flat state according to  claim 7 , wherein a DC voltage is intermittently supplied to said fan on said transfer path.  
     
     
         9 . A method for maintaining a plate member in a flat state according to  claim 8 , wherein 
 said supporting member is intermittently moved along said transfer path so that a DC voltage is supplied to said fan when said supporting member is stopped.    
     
     
         10 . A method for maintaining a plate member in a flat state according to  claim 9 , wherein 
 acceleration and deceleration of said supporting member intermittently moving along said transfer path are 500 cm/sec 2  or less.    
     
     
         11 . A method for manufacturing a disc by adhering two disc substrates together using an ultraviolet curable composition as an adhesive, comprising the steps of: 
 applying the ultraviolet curable composition onto at least a part of an adhering surface of at least one of said disc substrates;    radiating an ultraviolet light onto the applied ultraviolet curable composition;    superimposing said two disc substrates so as to sandwich the ultraviolet curable composition;    spreading the ultraviolet curable composition between said disc substrates; and    maintaining said two disc substrates in a flat state using a method for maintaining a plate member in a flat state as claimed in  claim 1 , said two disc substrates are considered as said plate member.    
     
     
         12 . A method for manufacturing a disc according to  claim 11 , wherein said disc is a digital versatile disc (DVD).  
     
     
         13 . A flatness maintaining unit for a plate member, comprising: 
 a supporting member having a flat surface provided with at least one hole penetrating through the flat surface; and    an air-suction device provided with said supporting member, said air-suction device drawing air to generate an airflow flowing from a front side of the flat surface towards a back side of the flat surface via the hole so that said plate member is retained on the flat surface of said supporting member when said plate member is placed on said supporting member.    
     
     
         14 . A flatness maintaining unit for a plate member according to  claim 13 , wherein 
 said plate member is a disc substrate,    said at least one hole provided with said flat surface of said supporting member is a first hole which is larger than a central hole of said disc substrate, and    at least a part of an outer periphery portion of said disc substrate is located outside an edge portion of said supporting member when said disc substrate is placed on said supporting member so that the center of said disc substrate is aligned with the center of said first hole.    
     
     
         15 . A flatness maintaining unit for a plate member according to  claim 13 , wherein 
 said plate member is a disc substrate,    said at least one hole provided with said flat surface of said supporting member is a first hole which is larger than a central hole of said disc substrate, and    the other of said at least one hole is provided with said flat surface located at a position where at least a part of the other of said at least one hole is covered by an outer periphery portion of said disc substrate when said disc substrate is placed on said supporting member so that the center of said disc substrate is aligned with the center of said first hole.    
     
     
         16 . A flatness maintaining unit for a plate member according to  claim 15 , wherein 
 the diameter of said first hole is larger than 15 mm,    said flat surface of said supporting member is provided with second holes at positions along the circumference of a circle having a diameter of 80 mm which is concentric with said first hole, and    at least a part of the edge portion of said supporting member is located inside a circle having a diameter of 120 mm which is concentric with said first hole.    
     
     
         17 . A flatness maintaining unit for a plate member according to  claim 15 , wherein 
 the diameter of said first hole is larger than 15 mm,    said flat surface of said supporting member is provided with second holes at positions along the circumference of a circle having a diameter of 80 mm which is concentric with said first hole, and    said flat surface of said supporting member is provided with third holes at positions along the circumference of a circle having a diameter of 120 mm which is concentric with said first hole.    
     
     
         18 . A flatness maintaining unit for a plate member according to  claim 13 , wherein a surface roughness Ra of the surface of said supporting member is about 3.0 μm or less.  
     
     
         19 . A flatness maintaining device for a plate member, comprising: 
 a flatness maintaining unit according to claim  13 ;    a transfer path along which said flatness maintaining unit moves;    a mounting device which places said plate member on the flat surface of said supporting member of said flatness maintaining unit at a first point on said transfer path, and    a removing device which removes said plate member from said supporting member of said flatness maintaining unit at a second point on said transfer path.    
     
     
         20 . A flatness maintaining device for a plate member according to  claim 19 , wherein 
 said transfer path is a circulation path; and    another plate member is mounted on said flatness maintaining unit, from which said plate member is removed at the second point, at the first point on said transfer path.    
     
     
         21 . A flatness maintaining device for a plate member according to  claim 20 , wherein a plurality of said flatness maintaining units are disposed on said transfer path at the same time.  
     
     
         22 . A flatness maintaining device for a plate member according to  claim 19 , wherein 
 an electric fan is integrally provided with said supporting member as an air-suction device, and    contacting electrodes which supply electric power to said fan are disposed on said transfer path.    
     
     
         23 . A flatness maintaining device for a plate member according to  claim 22 , further comprising: 
 a device which intermittently moves said flatness maintaining unit along said transfer path.    
     
     
         24 . A flatness maintaining device for a plate member according to  claim 23 , further comprising: 
 a control device which controls acceleration and deceleration of said supporting member intermittently moving along said transfer path so that the acceleration and deceleration are 500 cm/sec 2  or less.    
     
     
         25 . A disc manufacturing device which manufactures a disc by adhering two disc substrates together using an ultraviolet curable composition as an adhesive, comprising: 
 an application unit which applies the ultraviolet curable composition onto at least a part of an adhering surface of at least one of said disc substrates;    an ultraviolet light radiation unit which radiates an ultraviolet light onto the applied ultraviolet curable composition;    a unit which superimposes said two disc substrates so as to sandwich the ultraviolet curable composition;    a spreading unit which spreads the ultraviolet curable composition between said disc substrates; and    a flatness maintaining device for a plate member as claimed in  claim 19 , said two disc substrates are considered as said plate member.